1. Field of the Invention
The present invention relates to novel conjugated polymers, methods for their preparation and intermediates used therein, mixtures and formulations containing them, the use of the compounds, mixtures and formulations as semiconductor in organic electronic (OE) devices, especially in organic photovoltaic (OPV) and organic field-effect transistor (OFET) devices, and to OE and OPV devices comprising these compounds, mixtures or formulations.
2. Description of the Prior Art
In recent years there has been growing interest in the use of organic semiconductors, including conjugated polymers, for various electronic applications.
One particular area of importance is the field of organic photovoltaics (OPV). Organic semiconductors (OSCs) have found use in OPV as they allow devices to be manufactured by solution-processing techniques such as spin casting and printing. Solution processing can be carried out cheaper and on a larger scale compared to the evaporative techniques used to make inorganic thin film devices. State-of-the-art OPV cells contain a blend film of a conjugated polymer and a fullerene derivative, which function as electron donor and electron acceptor, respectively. In order to achieve highly efficient OPVs, it is important to optimize both the polymer (donor) and fullerene (acceptor) components and to find a material combination yielding an optimal bulk heterojunction (BHJ) morphology that supports efficient exciton harvesting and charge transport properties. Recent improvements in the efficiencies of single junction OPVs (efficiency ˜8-9%) have largely been due to the development of low-band-gap polymers, which are defined as polymers with an absorption onset at least 750 nm or more and with a band-gap of 1.65 eV or less.
A serious drawback of polymer and polymer/fullerene materials that have been suggested in prior art for use in OPV devices is that all high-efficiency OPVs have a relatively thin active layer (100-150 nm), which limits the light harvesting ability of the polymer/fullerene film and makes it challenging to apply such thin films to industry processes. When the thickness of the active layer is increased (e.g., to 300 nm), the fill factor (FF) of the cell typically suffers a dramatic decrease (below 60%), which results in poor efficiencies. The low FF and efficiency of thick polymer semiconductors (PSCs) are likely due to the limited charge transport ability of the polymer and impure polymer domains, among other factors. One way to achieve efficient thick-film PSCs is by obtaining morphologies that contain highly crystalline and pure polymer domains with excellent charge transport abilities. Obtaining a morphology with highly crystalline and pure, yet still reasonably small (e.g., 20 nm), polymer domains is a fundamental challenge.